The 24-month health certificate (CS24) is designed to identify health risks in a child’s environment and serves as an epidemiological tool for assessing, among other things, vaccination coverage (VC). Since 2007, the Bouches-du-Rhône General Council (CG13) has reported a decline in the number of CS24s returned to its offices. These certificates are used, among other things, to estimate vaccination coverage against diseases included in the national immunization schedule. The CG13 asked the Regional Unit of the French Institute for Public Health Surveillance (InVS) in the South (Cire) to better characterize the return rates of CS24 forms in order to guide awareness-raising efforts targeting physicians regarding the completion and submission of these certificates. Analysis of CS24 return rates in this department shows a significant decline, from 53% in 2007 to 36% in 2011, with relatively consistent rates across the various Departmental Solidarity Centers (MDS). The highest return rates were observed in the western part of the department and outside Marseille. The quality of data entry was impacted by changes to the vaccination schedule, which required modifications to the CS24 forms and IT applications, as well as a period of adjustment for healthcare professionals. A comparison of CV data calculated from CG13 raw data with adjusted data from the Directorate for Research, Studies, Evaluation, and Statistics (Drees) for the various vaccine types from 2007 to 2011 revealed similar estimates, suggesting that the adjustments made by Drees have little impact. Estimating CVs at the sub-departmental level requires caution due to potential reporting biases that vary by MDS. This study could be supplemented by a qualitative component to better understand the reasons for this decline in CS24 reporting among healthcare professionals. Providing feedback at the departmental level could prove useful by informing professionals about the outcomes and results of CS24s, as well as their impact on public health decisions.